An electrocardiogram signal indicating a change in electromotive force of heart is estimated by measuring a potential signal indicating a change in potential on a surface of a living body through electrodes attached to the surface of the living body. As illustrated in FIG. 1, the electrocardiogram signal includes waves having peaks called a P wave WP, a Q wave WQ, an R wave WR, an S wave WS, and a T wave WT at every beating. Time intervals between peaks of each wave in the electrocardiogram signal are used for diagnosis, test, or the like of disease. The heart rate is measured, for example, by acquiring the time interval between the peaks of consecutive R waves WR.
There are known living body state estimation apparatuses which acquire information indicating a state of a living body. As one of this type of living body state estimation apparatuses, a living body state estimation apparatus disclosed in Patent Literature 1 acquires an RR interval which is a time interval between peaks of consecutive R waves based on an electrocardiogram signal of the living body. The living body state estimation apparatus calculates an average value of the acquired RR intervals.
The living body state estimation apparatus calculates a first parameter based on a deviation from the average value for each of the RR intervals which are smaller than the average value among the acquired RR intervals. The living body state estimation apparatus calculates a second parameter based on a deviation from the average value for each of the RR intervals which are larger than the average value among the acquired RR intervals. Next, the living body state estimation apparatus acquires a ratio of the first parameter and the second parameter as information indicating asymmetry of RR intervals.
Patent Literature 1: US 2002/052557 A.